The present invention relates to a lubricating device for intermittently supplying a lubricating fluid to the portions to be lubricated in sliding portions of various elements for use in machining tools, industrial equipments and power machines.
There are known two types of conventional lubricating devices using plunger pumps. The first type lubricating device as shown in FIG. 1 of Japanese Patent Publication No. 59-19243(1984), for example, includes a transmission mechanism which reduces the rotational speed of a drive motor, converts rotational motion of the motor to reciprocal swing motion of a plunger of the plunger pump through a cam and a lever, and then transmits the reciprocal swing motion. The second type lubricating device is of a fixed displacement, variable pressure type having a gear pump and a plunger pump in combination as shown in FIG. 2 of Japanese Patent Publication No. 58-47596(1983), for example.
In any of those two types of lubricating devices, the plunger pump serves to deliver and supply a lubricating fluid to the portions to be lubricated, and the delivery amount of lubricating fluid is determined by the diameter of the cylinder and the shift amount of the plunger. The shift amount of the plunger through which it can move upward from the bottom of the cylinder is determined by shape and length of the swing lever as well as cam parameters in the former lubricating device, and by ON-OFF cycles of the drive motor corresponding to ON-OFF switching of a microswitch effected upon the distal end of the plunger striking against the microswitch in the latter lubricating device.
In the aforementioned lubricating devices, the delivery pressure of lubricating fluid directed to the portions to be lubricated is determined by the stored resiliency of a spring situated in the upper portion of the plunger. As the stored resiliency is varied with changes in the delivery amount (i.e., the shift amount of the plunger), the steady delivery pressure cannot be assured. Further, since in any of the aforementioned lubricating devices the spring resiliency is required to provide the minimum delivery pressure, several springs with different spring constants are needed to assure the desirous stored resiliency for a wide range of the delivery amount. The supply suspension time of lubricating fluid directed to the portions to be lubricated is determined by a speed reducing mechanism for operating the cam, which in turn shifts the swing lever, in the former lubricating device, and an electric timer is employed in the latter lubricating device. Therefore, a limitation is imposed in setting of the suspension time and the cost is increased, respectively.
With the latter lubricating device which employs a gear pump and a plunger pump in combination, a period of time in which a lubricating fluid of predetermined amount is stored in the plunger pump is varied dependent on viscosity of the lubricating fluid. For this reason, this type lubricating device cannot be used in those cases where the supply timing of the lubricating fluid should be determined accurately.